The present invention relates generally to alertness monitoring systems for detecting operator fatigue. More specifically, but without limitation thereto, the present invention relates to a device for monitoring eye activity to detect the onset of low alertness levels.
Loss of alertness associated with cognitive fatigue or boredom is an administrative and a safety concern for any system that requires sustained observation by a human operator. Monitoring human operators for signs of fatigue is important in transportation, security, and process control environments where lapses in attention may be disastrous. Methods for alertness monitoring have been proposed based on measures of operator actions, electro-encephalographic (EEG) activity, and measures of eye activity. Several eye activity parameters have been shown to be sensitive to drowsiness or to time on task, which is linked indirectly to the onset of drowsiness in monotonous task environments. For example, using electro-oculographic (EOG) techniques, it has been reported that blink duration and blink rate typically increase while blink amplitude decreases as a function of cumulative time on task. Other EOG studies have found that saccade, i.e. movements of the eye from one fixation point to another, frequencies and velocities decline as time on task increases.
Other recent studies have reported on eye activity relative to performance level in simulated transportation environments. Morris and Miller demonstrated in 1996 the sensitivity of EOG measures to fatigue in aircraft pilots during a 4 xc2xd-hour flight. Weirwille, Wreggit, and Knipling reported in 1994 that a measure of eyelid droop, i.e. the percentage of time that the eyelid covers 80 percent or more of the pupil, may be a useful component of eye activity to detect drowsiness during simulated driving tasks. Using video analysis techniques, other investigators have shown that pupil diameter increases as a function of drowsiness (Lowenstein and Lowenfeld, 1962; Yoss, Moyer, and Hollenhorst, 1970).
A disadvantage of the methods mentioned above is that they are generally obtrusive and require direct physical contact with the subject. Another disadvantage of these methods is that they require integration over several minutes, which rules out estimation of drowsiness in real time. A need therefore exists for a non-obtrusive eye activity monitor that does not require a mechanical or electrical connection to the subject and that can estimate drowsiness in real time.
The present invention is directed to overcoming the problems described above, and may provide further related advantages. No embodiment of the present invention described herein shall preclude other embodiments or advantages that may exist or become obvious to those skilled in the art.
An eye activity monitor of the present invention integrates multiple eye activity measures and applies them to general or custom alertness models to determine the onset of operator drowsiness in real time.
An advantage of the eye activity monitor of the present invention is that no physical contact with the subject is required.
Another advantage is that eye activity measurements may be made in a non-obtrusive manner, avoiding distractions that might impair the performance of the subject.
The features and advantages summarized above in addition to other aspects of the present invention will become more apparent from the description, presented in conjunction with the following drawings.